At present, several such electronic devices are in use, to which it is possible to connect various peripheral devices, e.g. to expand the properties of the electronic device and to produce auxiliary functions. For example, it is possible to connect peripheral devices, such as connection cards (e.g. PCMCIA cards), to laptop computers to connect the laptop computer to a local area network, a landline or wireless telephone network, etc. Furthermore, peripheral devices can be used to expand the memory of the laptop computer, to connect an external fixed disk, a CDROM station, or the like.
The MultiMediaCard™ Association is, among other things, developing a standard for memory expansion boards (MultiMediaCard™; MultiMediaCard™ is a trademark of Infineon Technologies AG). These memory expansion boards can be used in various portable electronic devices, such as wireless communication devices and communicator type devices, to expand the memory capacity.
Because the peripheral devices can be connected to a variety of devices, the power consumption of the peripheral device should not exceed the maximum power that can be supplied from the electronic device to the peripheral device. Otherwise, the operation of the peripheral device and/or the electronic device may be disturbed and the electronic device may even be overheated. On the other hand, the power consumption requirements of different peripheral devices may be very different, wherein manufacturers of electronic devices should provide for the maximum power consumption in the power supply of the peripheral device connection. Solutions are known, such as Nokia Communicator 9110/9210, in which the power supply of the peripheral device connection of the electronic device is provided with a relatively efficient regulator, for example in the order of 150 mA/3 V. Such an efficient regulator is a relatively bulky component, which may cause placement problems, particularly in portable electronic devices. The provision for the maximum power consumption will be unnecessary in such electronic devices, whose users do not use, in connection with the electronic device, such a peripheral device whose power consumption is close to the maximum power consumption of the peripheral device designed for the electronic device. On the other hand, another user of a similar electronic device may use such a peripheral device whose power consumption is in the order of the maximum power consumption of the peripheral device designed for the electronic device.
In some electronic devices and peripheral devices to be connected to them, the operating voltage is selected at the stage when the peripheral device is turned on, e.g. when the electronic device is turned on or when the peripheral device is connected. Thus, signalling will be performed between the electronic device and the peripheral device, for the electronic device to determine the level of the operating voltage required by the peripheral device and to select an operating voltage suitable for the peripheral device to the operating voltage line(s) of the peripheral device.
In said MultiMediaCard Association, a maximum limit has been proposed for the power consumption of memory cards of the MultiMediaCard™ type. Thus, in electronic devices supporting this standard, the provision is made to supply a defined maximum power to the peripheral device. Moreover, the power consumption of memory cards of the MultiMediaCard™ type should thus not exceed the defined maximum limit. Such an arrangement is difficult, for example, for the reason that the power consumption of new memory cards to be developed is limited to this maximum value, wherein it may be an impediment for the implementation of such memory cards whose power consumption cannot be made smaller than the selected maximum limit. If the maximum limit is set so high that the power consumption of other memory cards to be developed later on is also very likely to be smaller than this, it will mean that relatively efficient and large regulators must be used in electronic devices, perhaps unnecessarily.
The power consumption of the peripheral device is normally proportional to the clock frequency used in the peripheral device, wherein an increase in the clock frequency will increase the power consumption. In a corresponding manner, to decrease the power consumption, the clock frequency of the peripheral device can be decreased, if this is possible in view of the other functions of the peripheral device. However, the operating rate of the peripheral device will thus decrease, which is not necessarily desirable. Also, the bus width used in the peripheral device has an effect on how much power is consumed in the peripheral device.